The invention relates to detection of a locked axle condition on a locomotive propelled by AC traction motors. Specifically, the invention is a method for determining the existence of such a locked axle without employing a remote axle speed sensor. Locomotives used for hauling applications are generally equipped with speed sensors coupled to respective traction motors or to the axles driven by the motors. The speed sensor data or information may be used to detect a locked axle condition. If a locked axle condition occurs on a given axle while the locomotive is moving, the rotational speed of that axle decreases to zero, and all other axles rotate at the speed corresponding to the speed of the locomotive. Thus, a locked axle condition can be detected whenever a substantial difference in speed is sensed in one axle relative to the other axles.
In addition, when a speed sensor fails to supply reliable sensor data, a locked axle condition may be indicated in a system controller since existing controllers are not generally capable of detecting a failure in the speed sensor. When a locked axle condition is indicated, the operator generally must stop the train and visually inspect the axle or wheels for any discemable damage. If the visual inspection does not reveal any useful information, then the train may have to be rolled slightly to ascertain whether in fact the axle is locked or whether the condition was indicated due to a faulty speed sensor. If the latter is true, then the locomotive can be operated at lower speeds until the speed sensor and/or speed detection system is repaired. Stopping trains, inspecting axles and operating at lower speeds involve burdensome delays. Thus, there is a need for a low-cost method to reliably determine when a locked axle condition has actually occurred that does not employ axle speed sensors.
An exemplary embodiment of the invention is a method for detecting a potentially locked axle on a vehicle propelled by an AC motor. The method includes conducting a speed test by estimating axle speed and comparing estimated axle speed to measured vehicle speed. The existence of a potential locked axle condition is determined based on the comparing of estimated axle speed to measured vehicle speed. Additional tests are disclosed for determining a potential locked axle condition and a sensor fault condition.